Arctic Dinosaurs

Trek through Alaska to explore how dinosaurs once thrived in polar regions.
Airing July 27, 2011 at 9 pm on PBS
Aired July 27, 2011 on PBS

Program Description

(Program not available for streaming.) Most people imagine dinosaurs lurking in warm locales with swamps and jungles, dining on vegetation and each other. But "Arctic Dinosaurs" reveals that many species also thrived in the harsh environments of the north and south polar regions. NOVA follows two high-stakes expeditions and the paleontologists who push the limits of science to unearth 70 million-year-old fossils buried in the vast Alaskan tundra.

The hardy scientists shadowed in "Arctic Dinosaurs" persevere because they are driven by a compelling riddle: How did dinosaurs—long believed to be cold-blooded animals—endure the bleak polar environment and navigate in near-total darkness during the long winter months? Did they migrate over hundreds of miles of rough terrain like modern-day herds of caribou in search of food? Or did they enter a dormant state of hibernation, like bears? Could they have been warm-blooded, like birds and mammals? Top researchers from Texas, Australia, and the United Kingdom converge on the freezing tundra to unearth some startling new answers.

Transcript

Arctic Dinosaurs

PBS Air date: October 7, 2008

NARRATOR: High inside the Arctic
Circle, in one of the most unforgiving environments on the planet, two teams of
paleontologists investigate a 70-million-year-old mystery. They've unearthed
dozens of dinosaurs—adults and juveniles—their bones jumbled
together, fossilized, then locked in permafrost for eons, until now.

KEVIN
MAY (University of
Alaska Museum): Well, there's two pieces of
bone right here.

RON TYKOSKI (Museum of Nature & Science): It's as if somebody took 15
Pachyrhinosaurus, dumped them in a blender for 30 seconds and then poured all
the mess out into a large batch of concrete and let it solidify for 70 million
years.

NARRATOR: The startling discovery
that these ancient reptiles, "thunder lizards," lived and thrived in the arctic
has taken scientists by surprise.

ANTHONY
FIORILLO
(Museum of Nature and Science, Dallas): It challenges everything that we think we know
about dinosaurs.

HANS-DIETER
SUES
(Smithsonian Institution): Finding polar dinosaurs was important because it
provided whole new insights into the biology of dinosaurs.

NARRATOR: How did they survive in
such an extreme environment, and what was the real reason they were driven to
extinction?

ROBERT
SPICER (The
Open University, U.K.): There's a lot of questions out there. And it's not as simple as,
"Everybody died because a rock came in from space."

BOBBY
FITHIAN (Alaskan Permafrost
Miner): Fire in the hole!

NARRATOR: From millions of years in
the past, a story of survival against all odds: Arctic Dinosaurs, right
now on NOVA.

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NARRATOR: Early March, Alaska's
North Slope, the frozen Colville River: a team of scientists has pitched camp
here, at the base of these cliffs, willing to brave the perilous polar winter
to investigate a startling discovery.

KEVIN
MAY: There it is. A
Hadrosaur...looks like base of the tail. Success!

NARRATOR: They've unearthed dinosaur
bones near the North Pole. The animal was called Edmontosaurus, a gentle giant,
a 35-foot-long, four-ton, duck-billed plant eater, a member of the Hadrosaur
family, found in 70-million-year-old rock, a mere 50 miles from the Arctic
Ocean, where temperatures can drop as low as minus-60 degrees Fahrenheit.
According to conventional wisdom, it shouldn't be here, because this is how
dinosaurs are typically pictured: cold-blooded reptiles living in tropical
climes, not in cold, arctic environments like this one. And the Hadrosaur is
not alone.

In
two sites along Alaska's Colville River, paleontologists have recently
unearthed eight distinct species, represented by hundreds of fossils.

ANTHONY
FIORILLO: On
this table are examples of the biodiversity of the animals—the vertebrate
animals—that we've found up on the North Slope. And we have a variety of
meat-eating dinosaurs, and this is the left-front jaw of an animal called
Gorgosaurus.

NARRATOR: Thirty feet long, almost
three tons; mainly a match for its fearsome cousin, Tyrannosaurus rex,
Gorgosaurus was at the top of the food chain. In competition: Troodon, six feet
long, 150 pounds—small but ferocious; and Dromaeosaurus, a wolf-like
two-legged hunter, which may have had feathers as insulation.

ANTHONY
FIORILLO:
And here we have a horn core from our Pachyrhinosaurus.

NARRATOR: ...a massive four-ton
plant eater, with a broad, bony frill protecting its neck, an elongated skull
with a beaked mouth, and a thick bone above the nasal opening;
Pachycephalosaurus, a two-legged plant-eating brute, with a thick, bony dome on
its head, possibly used for combat or defense; and Thescelosaurus, another
two-legged animal thought to be a plant eater. The unexpected discovery of so
many species living in the arctic is leading scientists to rethink old
assumptions about dinosaur biology.

HANS-DIETER
SUES: The
traditional view was that dinosaurs were all overgrown reptiles that lived
under tropical conditions. When we found polar dinosaurs, however, it was
driven home to everyone that dinosaurs could live under different...and thrive
under very different climate conditions.

NARRATOR: Scientists long believed
that dinosaur biology resembled that of cold-blooded reptiles like crocodiles,
animals that require warmth to survive and cannot withstand prolonged exposure
to temperatures below freezing. But not one crocodile fossil has been found
along the Colville, which suggests that polar dinosaurs found a way to adapt to
an environment that their cold-blooded cousins couldn't tolerate. But how?

Luckily
for the scientists, many important clues are preserved in the rock. When these
animals died, layer upon layer of sediment covered their bodies. Minerals
slowly replaced bone tissue to create fossils. Then, 45 million years ago,
geologic forces began to uplift the ground, exposing the edge of the fossil
layer along these frozen cliffs.

KEVIN
MAY: Well, there's two pieces of
bone right here. There's another piece of bone.

KEVIN
MAY: There's enough bone here
already that would indicate that this very well may be the Liscomb bed.

NARRATOR: It was here, in 1961, that
Shell Oil geologist Robert Liscomb came across a large fossil. He sent the
specimen back to his office, intending to have it classified by a
paleontologist.

ANTHONY
FIORILLO:
Unfortunately, Liscomb died the next year, in a rock slide, so they were in a
Shell warehouse until about the mid-1980s, when Shell was cleaning house, and
they sent them to the U.S.G.S. There, a paleontologist by the name of Charles
Repenning, found the bones and immediately recognized that they were dinosaur
bones.

NARRATOR: Now, scientists Tom Rich
and Kevin May are about to go deeper into the Liscomb bone bed than anyone has
ever attempted.

TOM
RICH: My gut feeling is that it's
going to go a lot further back than three to four meters.

BOBBY
FITHIAN: Think that black layer could
very well be the fossilized layer?

NARRATOR: With the help of seasoned
Alaskan gold miner Bobby Fithian, they will spend the next month blasting a
tunnel into the permafrost. Once inside, they will dig down into the bone
bed—the rock layer—where fossils, if they're there, lie packed together,
protected from the elements.

They
begin with a set of relatively small charges.

BOBBY
FITHIAN: Fire in the hole!

NARRATOR: The goal is to open a
passageway about a foot above the fossil bed, but no closer. The worry is that
if they don't angle the blasts just right, they'll destroy the treasures they
came to retrieve.

TOM
RICH: Take a look at this distal
tibia. That was found right down here, at this level here.

NARRATOR: So far, they seem to be
right on target.

TOM
RICH: It's a good start.

NARRATOR: Blasting for fossils is an
unusual way to do paleontology, but not for Rich. He was one of the first
scientists to discover polar dinosaur fossils, not in Alaska, but at the
opposite end of the world.

TOM
RICH: I don't mean to pat myself on
the back, but as far as trying new techniques and it worked: 20 years ago, I
cut a tunnel. I cut a tunnel in Australia.

NARRATOR: There, he used dynamite to
expose a narrow fossil layer buried deep in the rock. That bone mine yielded
thousands of fossils, mostly well-preserved small pieces, proof that 100
million years ago, dinosaurs lived near the South Pole, an environment even
colder than this one, near the North Pole, where he's trying, again, to find
dinosaurs.

KEVIN
MAY: Man, we've got a small bone
here. Look at this.

TOM
RICH: Where?

KEVIN
MAY: Right in here. Yeah, this
little...

NARRATOR: Paleontologist Kevin May
has searched for fossils all over Alaska, but this is his first tunnel, and
he's excited by the Hadrosaur bones that are beginning to be exposed as they go
deeper.

KEVIN
MAY: This is exactly what we came
here for. This is the best I've ever seen this stuff. I just am blown out on
this one.

TOM RICH: Yeah, so we don't need to go deeper, we
just need to go straight in at about this level. Give yourself, maybe, 10
centimeters above what is obviously a fossil layer, into this stuff.

NARRATOR: The initial digging to
establish the entrance to the tunnel has already unearthed some large bones.

KEVIN
MAY: That's definitely a rib.

NARRATOR: But most are in poor
shape.

KEVIN
MAY: Some type of long bone here.
Unfortunately, it's fairly well powdered.

NARRATOR: Because they were lying
close to the surface, the fossils have been broken and worn by the freeze-thaw
cycle, the punishing effect when water seeps into the ground and then expands
when frozen, cracking open rocks. The purpose of the tunnel is to dig deep into
the permafrost, which is not prone to those seasonal changes, and hopefully
find better preserved, smaller and more delicate bones.

TOM
RICH: When we get in, what we
hope...20 meters, we're going to be beyond that, so we're going to see bones
for the first time that's never been through that.

NARRATOR: With the entrance set
safely above the fossil layer, they give Bobby Fithian the go-ahead to complete
the blasting.

When
they're finished, the tunnel stretches a remarkable 65 feet into the cliff,
laying bare rock that hasn't seen the sun for tens of millions of years.

BOBBY
FITHIAN: We're going to finish
securing the tunnel and supporting this ground.

NARRATOR: The team has successfully
completed the first phase of their project. The delicate work of excavating the
bone bed will begin in five months time, during the arctic summer when the
weather is milder and the sun remains above the horizon nearly 24 hours a day.

BOBBY
FITHIAN: There isn't any reason for
this tunnel not to be here at least a hundred years from now if you take care
of it. You've got a nice tunnel. You're going to find some dinosaurs.

NARRATOR: For Tom, this is the culmination
of years of struggle, and he knows that without the skills of the Alaskan
miners, it could never have come to pass.

TOM
RICH: I'd like to thank all of you.
You know, you guys have helped me achieve something I've been trying to get to
for 18 years.

NARRATOR: Though the goal this time
was merely to build the tunnel, their work paid an unexpected dividend,
Hadrosaur bones. These duck-billed plant-eaters appeared about 145 million
years ago and were one of the most successful groups living, right up until the
time that all dinosaurs died out, around 65 million years ago.

Hadrosaurs
may have owed their success to several important adaptations. They were one of
the first large animals to evolve fleshy cheeks and hundreds of teeth that were
continually replaced, features that made it possible for them to chew their
food instead of just biting and swallowing, as other creatures did. They also
built nests and apparently tended their eggs like brooding birds.

Hadrosaurs
are the most common dinosaur at the Liscomb bed. But 28 miles upriver from the
tunnel, atop a 300-foot cliff, a second team of paleontologists has made
another remarkable find: a mass grave containing at least four species of
dinosaur, including Gorgosaurus, Edmontosaurus, Troodon and Pachyrhinosaurus.

ANTHONY
FIORILLO:
This is the most diverse assemblage of fossil...of dinosaur bones here on the
North Slope. It's got a variety of kinds of animals. It's got tremendous bone
density. There's an abundance here like I've never...would never have believed.

NARRATOR: Tony Fiorillo and his team
are doing paleontology the old-fashioned way, with picks, shovels and grim
determination.

ANTHONY
FIORILLO:
There's some sites I've worked, in the lower 48, where a chimpanzee with a
Popsicle stick can work the localities. This quarry is not one of those
localities.

NARRATOR: It's late summer, but this
hardly feels like a vacation. The treacherous climb, the frozen ground, the
freezing rain, are a daily trial. But it's all been worth it because Tony has
just found the crown jewel of the Colville: a massive skull, flattened but
otherwise intact.

ANTHONY
FIORILLO:
This is the right side of the face.

NARRATOR: It takes a trained eye to
see the shape embedded in the rock. But to Tony, it's crystal clear.

ANTHONY
FIORILLO:
This is a skull of a horned dinosaur. It's upside down so you're looking at the
right side or the right cheek of something that we've been calling
Pachyrhinosaurus.

NARRATOR: Pachyrhinosaurus: the
horned dinosaur, a relative of Triceratops, previously known only to live much
farther south. And there are others.

ANTHONY
FIORILLO:
There's 14 individuals of the horned dinosaur in this little pit so far.

NARRATOR: Finding so many
Pachyrhinosaurus in one spot is like stumbling on an elephant graveyard.
Seventy-million years ago, something happened that deposited the bodies of more
than a dozen massive animals in this one spot. The river below offers a clue.

ANTHONY
FIORILLO: A
density of bone so high that it's easy to envision this being a jam in a river
channel. These animals were transported downriver somewhere. And presumably
they created their own little logjam, except there was a bone jam in a river
channel.

NARRATOR: But as long as the skull
remains in the ground, there's little that Tony can learn from it. So the team
is working to remove the half-ton piece of rock that encases it so that they
can transport it back to their lab in Dallas, Texas.

Step
one: dig out the skull without breaking it...

ANTHONY
FIORILLO:
...is move some of this rock out of the way here and up here.

NARRATOR: ...encase it in a
protective jacket, made of burlap and plaster, and then airlift it to safety.
That's the plan, but nature isn't cooperating.

KENT
NEWMAN
(Fossil Preparator): Right now, the weather is killing us. It's mid-30s, it's snowing, and
we're in the arctic. And so, mixing plaster and this kind of moisture and with
snow and high humidity, it's problematic.

On
three; one, two, three. Watch it, watch it, watch it.

We'll
plaster that hole over and then we can hoist it out with a chopper.

NARRATOR: When the helicopter
arrives, they worry that the plaster hasn't fully cured.

ANTHONY
FIORILLO:
What do you think?

KENT
NEWMAN: It's not giving off any more
heat so it's hydrated. It's hardened as much as it's going to get.

NARRATOR: But the helicopter is on a
tight schedule. It's due to deliver its load to an airstrip further upriver.
From there, the skull will travel by plane to Fairbanks and then 4,000 miles,
by truck, to warm and sunny Dallas.

ANTHONY
FIORILLO:
Keep our fingers crossed.

NARRATOR: Tony knows he's made a big
find. But because rock surrounds the skull, he doesn't know yet the condition
of what's inside. So when the jacket arrives in Texas, Tony's colleague, Ron
Tykoski quickly begins the painstaking work of removing the debris that
surrounds the large skull. He's almost immediately surprised. The rock around
the skull is filled with bones, bits and pieces from more than one
Pachyrhinosaurus.

RON
TYKOSKI: A wonderfully intact
vertebra, part of the spine of this animal.

NARRATOR: This bone is of particular
interest. They've already found several others at the same site, but until now,
they weren't completely sure which dinosaur species it belonged to.

RON
TYKOSKI: This is a point where the
skull attaches to the first vertebra of the neck in a beautiful ball and socket
joint. And we have at least 15 of these, from this particular quarry. It's as
if somebody took 15 Pachyrhinosaurus and dumped them in a blender for 30 seconds
and then poured all the mess out into a large batch of concrete and let it
solidify for 70 million years. Everything is completely jumbled about. Bones
are oriented in all sorts of different directions, and nothing's connected.

NARRATOR: Finding so many
Pachyrhinosaurus tells Tony that these wide-ranging animals, found throughout
North America, lived in large numbers on the North Slope. But the bones don't
say how they lived, or what conditions were like during the toughest time of
year.

ANTHONY
FIORILLO:
What did they do during the wintertime? How was life up here the same or
different than what we see in the lower latitudes?

NARRATOR: Scientists have long known
that the Earth's climate was generally warmer during the time of the dinosaurs.
But how warm was the polar climate 70 million years ago? Was it hot enough to
be considered tropical, and were the seasons as extreme as they are in the
arctic today?

British
paleobotanist Robert Spicer may have solved one important piece of the puzzle,
with the help of ancient plants.

ROBERT
SPICER: When I find a fossil leaf, it
tells me something, it's like a messenger from the past.

NARRATOR: He made his first trip to
the Colville River in 1976.

ROBERT
SPICER: It was known that there was a
rich flora there, but what I didn't realize was just quite how abundant it was.
So we'd land and run over to the outcrop and start hammering away, and there
were the leaves.

NARRATOR: Since then, Spicer has
amassed one of the world's most impressive collections of arctic botanical
fossils from the Late Cretaceous.

ROBERT
SPICER: This collection here is
fairly typical of the kind of fossils we find throughout the Late Cretaceous of
the North Slope. Now, what we have here is a 90-million-year-old cycad.

NARRATOR: Cycads are tropical and
indicate warm conditions.

ROBERT
SPICER: This one here, this is a
conifer.

NARRATOR: Conifer trees are found in
a variety of climates. Measuring up to 30 feet tall, they were common on the
North Slope.

ROBERT
SPICER: This is a fern. These are the
sorts of things that your knees would brush past as you walked through the
Cretaceous forest. This, here, is quite unusual. It's a leaf which has got a
smooth edge to it, it hasn't got any teeth. And this is typical of the kinds of
leaves that we tend to find in warm environments today.

NARRATOR: As his collection grew,
Spicer had a hunch that he could use these leaves to deduce the temperature of
the arctic, 70 million years ago.

It
was an idea based on a simple observation that allowed him to decode the secret
language of leaves. In hot tropical climates, the edges of leaves are smooth,
but in colder climates, they tend to have serrated edges.

ROBERT
SPICER: Well, when we look at leaves
such as these, you can see that the edges of the leaf have got teeth on them,
and it's very jagged. And, in fact, if you look at any of the tree species
around here, in this relatively cool climate in the U.K., you'd be very
hard-pressed to find a significant number of leaves that have got smooth edges
to the leaves.

NARRATOR: Spicer believes that these
serrations evolved to help plants circulate water and nutrients. In hot
climates, moisture evaporates from leaves, causing water to rise up through the
roots. But if the temperature drops, evaporation and circulation ceases.

ROBERT
SPICER: Now, in those situations, the
plant can't evaporate water from the leaf, so it can't suck water out from the
ground. And, of course, the plant needs the fluid going through the plant body
to move nutrients.

NARRATOR: But the serrations in
leaves growing in cool climates solve that problem because at the tip of each
tooth is a small gland that aids circulation.

ROBERT
SPICER: So in a cool environment, the
plant actually pumps water out through the teeth.

NARRATOR: The real breakthrough came
when Spicer realized that he might be able to pinpoint the temperature of the
Late Cretaceous using his fossils.

ROBERT
SPICER: It's the proportion of tooth
leaves and non-tooth leaves that we see in a particular place, living today or in
a fossil assemblage, that gives us an idea of the relative warmth, the average
annual temperature during the year.

NARRATOR: He and his team spent
years comparing leaf shapes to climate data in more than 170 locations around
the world. It was a massive undertaking. But in the end, he was able to create
a statistical model that ties leaf-tooth patterns to temperature.

ROBERT
SPICER: We can tell what the average
annual temperature was, at a given place, to within plus or minus one or two
degrees Celsius, which is, when you actually look at it in detail...is about as
precise as many modern day meteorological observations are.

NARRATOR: When Spicer examined his
fossil collection, he discovered a match between those ancient arctic leaves
and leaves found today in Southern Alaska, a temperate climate, very different
from the barren tundra today. The model indicated that the average annual
temperature on the North Slope was about 42-degrees Fahrenheit, 30 degrees
warmer than it is there today. But that number is deceptive because at high
latitude, the yearly highs and lows are far apart.

So,
while the dinosaurs would have enjoyed summer temperatures in the 70s, winters
were likely cold enough to produce snow and even ice.

On
the Colville, summer temperatures are now nearly 100 degrees above the frigid
lows of late March. The dinosaur mine has been sealed for five months. Now it's
time to find out if there's anything inside.

KEVIN
MAY: Grab a shovel.

NARRATOR: This is not what they
hoped to find. The portico built by the miners held up, but the eroding cliff
has poured in around the edges, nearly burying the entrance. And there's even
worse news.

KEVIN
MAY: This is sort of bad news,
here. It's like we've got impounded inside the tunnel, that water, flowing
beyond our vapor barrier, so there must be standing water on the other side of
this hole.

NARRATOR: During the spring thaw,
the river rose an incredible 25 feet and flooded the tunnel.

KEVIN
MAY: Oh, joy. The bad news is we
got a mess.

NARRATOR: There is some good news.

KEVIN
MAY: This is beautiful. That is
fine. We're going to be safe in here. There's no yield at all.

NARRATOR: The walls and ceiling are
frozen solid. It's like standing inside a refrigerator cooled by
million-year-old permafrost.

During
the winter excavation, the team didn't have time to explore the fossil bed, and
now, because of the flood, the tunnel floor is hidden beneath at least a foot
of ice. And there's only one way to get it out. It will take days of brute
force labor to clear out the tunnel.

The
outside temperature may be warm enough for the scientists to work in
shirtsleeves, but this is not a hospitable place. The river temperature is
barely above freezing, and the arctic landscape is barren.

If
they were alive today, herds of dinosaurs could not have survived in a place
like this. What was their polar summer like 70 million years ago? That's the
question that Steve Hasiotis has set out to answer. He's a paleoichnologist.

NARRATOR: He studies impressions
preserved in rock, which are often the only record left by birds, insects,
worms and other animals too small or delicate to have become fossilized themselves.

STEVE
HASIOTIS: These
are just basically associated with things like horsehair worms.

NARRATOR: Using Alaskan fossils from
the Late Cretaceous, he's cataloguing the insects and other animals present in
Alaska, to measure the diversity and health of the dinosaur ecosystem.

STEVE
HASIOTIS: Hi,
guys, grab some gear. We do it by looking at the similar kinds of traces and
scratches and trail patterns made by animals and environments today, and then
we can take that information, look for the similar patterns in the rock record.

NARRATOR: Today, he's brought some
fossil impressions to a riverbank near Lawrence, Kansas. With the help of his
graduate students, he will try to match the trails made in the
70-million-year-old rock to those made just days or hours ago by modern
animals.

STEVE
HASIOTIS: Great
trail right there. Holy smokes! I think these are these mud-loving beetles,
where the ceilings of them have collapsed. The bird tracks here, and
then these worm trails here—this is the association that we're seeing up
in the arctic.

NARRATOR: From the modern day
animals on the bank of the Kansas River, a snapshot of a very similar
environment in ancient Alaska begins to emerge, and he's sharing his insights
with Tony Fiorillo.

STEVE
HASIOTIS: On
this, here, you've got about four or five or five different trackways, here,
and trails: ones that are slightly larger are aquatic earthworms; totally
fantastic hopping trails of a grasshopper or a cricket; this other thing, here,
is a crawling trail that's reminiscent of a beetle.

ANTHONY
FIORILLO: So
you got worms, beetles and some sort of cricket-like thing. Does that help
fine-tune the environment that these things were in?

STEVE
HASIOTIS: This
had to be, probably, in the height of the summer or near the end where it's
very warm. There's a high diversity, low-lying water, swampy areas, nice large
lake plain or lake margin exposed.

NARRATOR: That means a rich
ecosystem in the summer, capable of supporting creatures of all sizes and a
much greater diversity of plants and animals than is found in Alaska today.

STEVE
HASIOTIS: Picture
yourself standing on this lake shoreline. It's warm, sunny; there are herds of
duck-billed dinosaurs and other kinds of plant-eating dinosaurs along the lake,
eating vegetation like horsetails, gingkoes, the flowering plants; an abundance
of flying insects and crawling insects on the shoreline, in the water; Theropod
dinosaurs—large ones like T. rex, smaller ones like Troodon—in
there, hunting these plant-eating dinosaurs.

HANS-DIETER
SUES: The
good times of the year, when it was not dark and cool, it probably would have
been very similar to what we now see in the southeastern United States, with
lots of conifers, lots of flowering plants. In fact, the Late Cretaceous,
except for the dinosaurs, would not have been an unfamiliar environment to us.

NARRATOR: Conditions were mild
during the long bright summer days, but the winter would have been much more
challenging. Because they're so close to the Earth's axis, the
poles—North and South—experienced the most dramatic seasonal
changes.

At
the height of summer, when the North Pole is tilted towards the sun, the North
Slope enjoys a month of constant daylight. But in the depths of winter, when
the North Pole is tilted away from the sun, the North Slope spends six weeks
each year in near total darkness. The continents continually drift, and because
the North Slope used to be even closer to the North Pole, 70 million years ago,
the extremes were even more pronounced.

ROBERT
SPICER: The present location of the
Liscomb bone bed—that current latitude of about 70 degrees north—at
the time the dinosaurs were living, it was closer to 85 degrees north.

NARRATOR: Today, the North Slope is
1,500 miles from the North Pole, but 70 million years ago, it was four times
closer, a mere 350 miles, with four months of darkness during the long winter.

In
thin slices of fossilized trees, Bob Spicer sees how the darkness affected the
plant-eating dinosaurs' food supply. Under the microscope, individual cells are
visible, showing a pattern of growth rates.

ROBERT
SPICER: The tree rings show that in
the summer, the trees were very happy, they were growing quite rapidly.

NARRATOR: The light colored cells
were produced during the bright summer months.

ROBERT
SPICER: And as the season progresses,
the walls get thicker, the color goes browner, until, at the end of the growing
season, the cells are really quite small. Then we get no more cells; the tree
goes into dormancy.

NARRATOR: The summer growing season
was long and active, but once winter arrived, everything stopped.

ROBERT
SPICER: Now, what that means is that
it was dark and there wasn't a lot to eat.

NARRATOR: For plant eaters, the food
supply would be reduced to decaying plants, roots, even bark—hard
times—but not necessarily for meat eaters, like Troodon. Troodon may have
had an adaptation that would have turned the liability of darkness into a
killer's asset.

Tony
recently found a fragment of a young Troodon skull, which shows that the animal
had unusually large eyes and an enlarged optic lobe in the brain.

ANTHONY
FIORILLO: So
the brain would be in this cavity right here. We've just caught the beginning
of where that brain is enlarged to accommodate the optic region of the brain.

NARRATOR: Troodon's enhanced visual
system may have allowed it to hunt at night. And it's not the only species with
those features. In 1989, Tom Rich named Leaellynasaurus, found near the South
Pole, another small meat-eater with unusually large eyes. With food scarce, the
large herbivores would need to conserve energy. They would have been torpid,
sluggish—easy prey. But maybe the plant-eaters didn't hang around.
Perhaps when the season changed, they struck out in search of better
conditions.

HANS-DIETER
SUES: There's
even the suggestion that some of these animals have gone through annual
migrations. It's not inconceivable that these huge herds, particularly of the
large plant-eating dinosaurs, migrated over huge distances—much like many
modern mammals do today—in search of forage.

NARRATOR: Migration is an important
survival strategy in today's arctic. As summer ends, caribou herds migrate
south to their winter ranges. The distance is about 400 miles as the crow
flies, but, because the caribou don't travel in a straight line, the journey
can stretch to thousands of miles.

Dinosaurs
would have had an even longer journey. Because the North Slope was much closer
to the pole 70 million years ago, to escape the darkness, they would have had
to walk 5,000 miles, nearly twice the distance from New York to Los Angeles.

According
to Tony Fiorillo, some animals wouldn't have been able to make the trek. He's
compared the relative size of juvenile Hadrosaurs to adults, to determine if
the young were physically capable of keeping up with a herd on the move.

ANTHONY
FIORILLO: We
argued, through a biomechanical analysis of the juvenile duck-billed dinosaurs,
that they were too young or too small to make any long-distance migration. So,
therefore, we argued that these animals lived here year 'round.

That
opened up a whole bunch of interesting biological questions, like how did they
survive the seasonality?

NARRATOR: Tony's evidence has
important implications for a long-running debate about dinosaur biology. Were
they cold-blooded like lizards or warm-blooded like mammals?

Cold-blooded
animals cannot long endure low temperatures. They seek external heat sources to
power their metabolisms. Warm-blooded animals can generate heat internally to
keep a constant body temperature, and many warm-blooded animals are found in
cold climates. And there is strong evidence that dinosaurs were the ancestors
of modern birds, which are also warm-blooded, but so far, no conclusive answer
about dinosaurs.

Kevin
May's Hadrosaur bone could add clarity to the debate. It's now in a lab, in
South Africa, where Professor Anusuya Chinsamy-Turan is examining the bone for
clues about dinosaur metabolism.

ANUSUYA
CHINSAMY-TURAN:
(University of Cape Town): You're looking at a bone that is 70 million years old.
What we see here are these interesting structures that tells us about how fast
this bone formed, about organization of the bone tissue.

NARRATOR: The bones of warm-blooded
and cold-blooded animals form differently. Reptile bones grow rapidly when
conditions are favorable, but when food is scarce or temperatures drop, growth
ceases. That start-stop pattern of development leaves telltale markings in the
bone, similar to the rings in tree trunks.

ANUSUYA
CHINSAMY-TURAN: These alternating rings of growth that we see in reptiles, they tell us
that these animals...their growth is dependent on seasonality.

NARRATOR: Birds and mammals,
however, grow differently. They are not as sensitive to seasonal changes. They
add new layers of cells more rapidly and continuously. In warm-blooded
animals...no growth rings.

Because
the Hadrosaur was a dinosaur and because the Poles experienced the most extreme
seasonal swings on the planet, Anusuya expected that the bone would show
pronounced growth rings. But instead, she had a surprise.

ANUSUYA
CHINSAMY-TURAN: I don't see the growth rings that I would have expected in an animal
that would have been affected by seasonal climatic conditions.

NARRATOR: The Hadrosaur bone more
closely resembled the bone of a mammal or bird. That suggests that the
Hadrosaur did not hibernate or slow down during the winter. It was active all
year round.

ANUSUYA
CHINSAMY-TURAN: I suspect that perhaps this animal was very well adapted to the
environment in which it lived.

NARRATOR: For some scientists,
thinking of dinosaurs as warm-blooded is the only explanation that makes sense.

HANS-DIETER
SUES: If
they're warm-blooded, you can see them surviving in this kind of climate, much
as modern mammals and birds do in the arctic today.

NARRATOR: Today, biologists
increasingly understand that there exist degrees of warm-bloodedness and
cold-bloodedness in the animal world. It's not always one or another. Dinosaurs
likely had their own unique solution to the body temperature problem, which allowed
them to survive for millions of years in the toughest seasonal conditions their
world had to offer.

At
the height of summer, the sun stays above the horizon nearly 24 hours a day.
Work has continued around the clock to clear the debris. Now is the time to
find out if the bones buried inside are better preserved than those found in
the cliff face.

Kevin
makes the most of the short time he has left. Jackhammers give way to precision
instruments.

KEVIN
MAY: We have this frozen unbroken
matrix that we're able to shave off layer by layer, and it's not flaking apart.
So you could not do this outside. You couldn't do it outside the permafrost.

NARRATOR: Almost immediately, the
team finds several extremely well-preserved bones, more delicate than any of
the bones they found outside the tunnel. Kevin May suspects that they may be
from a new species.

KEVIN
MAY: Well, it looks like we have
two tail vertebrae and then a flat piece of a rounded bone here.

NARRATOR: It will take years to
fully explore the tunnel and to complete the catalogue of arctic dinosaurs. To
date, Tony's Pachyrhinosaurus skull remains one of the largest specimens to
come from the Colville.

KEVIN
MAY: Yeah, it looks pretty good.
It is busted up a little bit so we'll have to keep our fingers crossed, but
getting that stuff out of the way, you can really...this is really nicely
defined now. And that's a skull.

NARRATOR: But despite its poor
condition, the skull and all the other fossils, miraculously preserved for 70
million years, reveal a fascinating chapter in the history of the Earth.

Two-hundred-thirty-million
years ago, the Earth was even warmer than it was at the end of the age of
dinosaurs. Those conditions fostered a great flowering of diversity, including
the evolution of dozens of species which came to dominate the land, the air,
the water, and eventually filled every corner of the globe.

And
then, 65-million years ago: a devastating blow to the planet...a massive
asteroid impact. The prevailing theory is that the resulting explosion threw
massive clouds of gas and ash into the air and plunged the Earth into a global
winter. The theory held that dinosaurs, tropical
animals, were unable to cope with the darkness and the cold that followed. But
the discovery that dinosaurs already lived in non-tropical conditions, enduring
long periods of darkness, suggests that there must be more to the story.

ANTHONY
FIORILLO: I
think that one of the values of our work is that it is suggesting that a
catastrophic end to the Cretaceous did not kill off the dinosaurs.

NARRATOR: But if the asteroid alone
didn't wipe out all dinosaurs, what did? According to the fossil record, 70
million years ago, five million years before the impact, the number of dinosaur
species around the world was already shrinking.

ROBERT
SPICER: As we go through the Late
Cretaceous, diversity seems to decrease. And it's a general truism of evolution
that the more biologically diverse you are, the more robust and able to cope
with environment change you are.

NARRATOR: Before the asteroid, the
writing had already been on the wall. Continents were on the move. Air and
water circulation patterns were changing, causing global temperatures to fall.
The planet was slowly evolving into the world we know today, a world in which
dinosaurs would not be able to thrive.

HANS-DIETER
SUES: I
think it's an instance where this huge impact that created the Chicxulub
crater, on the Yucatan Peninsula of Mexico, was basically, sort of, almost the
icing on the cake.

NARRATOR: The fossil record cannot
tell us how long dinosaurs survived after that terrible catastrophe, but arctic
dinosaurs, far removed from the disaster, could have been among the last
survivors in their changing world.

On
NOVA's Arctic
Dinosaurs Web site, watch any part of this program, go behind the scenes and
more. Find it on PBS.org.

Museum of Nature and Science, Dallas
University of Alaska Museum of the North
Museum Victoria
Bureau of Land Management, Arctic Field Office
National Park Service, Alaska Region
National Science Foundation, Office of Polar Programs
Smithsonian Institution
Monash University
University of Capetown
Open University, UK
University of Kansas
Australian Research Council
Conoco Phillips - Alaska
Pat Vickers-Rich
Amanda Hanson
Anne Pasch
Cindy Adkins
Aldona Jonaitis
Dennis 'Moose' Cunningham
Chris Scotese
Ron Blakey
John Searcy
Sharma Family
Umiat Social Club
ASV inc
Wrights Air Service

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